1. Field of the Invention
The present invention relates generally to an apparatus for permeating an irradiated light wherein the apparatus can widely be employed for an exposing equipment, a drying equipment, a printing equipment or the like photographic equipment which are employable for forming a pattern on a printed circuit board, for photographically making a printing plate for printing operations, for drying various kinds of organic materials such as an optically hardenable type paint, a resin, an ink, a varnish or the like material or for forming a hardened film. More particularly, the present invention relates to an apparatus for permeating an irradiated light wherein the apparatus is arranged at the intermediate position in an optical passage between a light source and an object to be irradiated with a light so as to remove heat rays and undesirable wavelength components in the irradiated light and moreover effectively prevent an adverse effect due to bubbles in a cooling liquid for cooling the apparatus.
2. Description of the Related Art
With respect to the exposing equipment for forming a pattern on a printed circuit board, the ultraviolet ray irradiating equipment for hardening a resin or the like apparatus, various kinds of proposals have been heretofore made for cooling means in the form of liquid type direct cooling means or forcible air-cooling type cooling means so as to elongate the running life of a discharge lamp. However, a sufficient quantity of research works have been not conducted with respect to a light permeating apparatus for suppressing thermal expansion of an object to be irradiated with a light and removing undesirable wavelength components in the irradiated light for the purpose of exhibiting and maintaining a normal function for a photosensitive material (so-called indirect cooling means).
To facilitate understanding of the present invention, a typical conventional light permeating apparatus will be described below with reference to FIG. 17 and FIG. 18. The conventional apparatus includes as essential components an opposing pair of light permeable plates 1 made of quartz or hard glass, a box-shaped casing 3 for defining a flat space 2 inside of the light permeable plates 1, a liquid supply tube 6 attached to the fore end 4 of the casing 3 and a liquid discharge tube 7 attached to the rear end 5 of the casing 3. When an irradiated light 8 permeates through the apparatus, the light permeable plates 1 absorb heat rays in the irradiated light 8. As the light permeable plates 1 are heated up to an elevated temperature by thermal absorption of the heat rays, they are cooled by a cooling liquid flowing through the space 2 (the flowing of the cooling liquid in the space 2 being represented by arrow marks a in the drawings).
However, it has been found that the conventional apparatus has the following problems.
(i), Since the apparatus is placed in the horizontally laid state at the intermediate location in an optical passage between a light source and an object to be irradiated with a light (representing the state as shown in FIG. 17), bubbles 10 in the cooling liquid are increasingly grown in size and floated up as a temperature of the cooling liquid is elevated during practical use of the apparatus. As is best seen in FIG. 17, the enlarged bubbles 10 adhere to the lower surface of the upper light permeable plate 1 and vibrantly move as the cooling liquid flows in the a marked-direction, whereby an optical passage of the irradiated light 8 is turbulently affected, causing formation of a clear image on a photosensitive material to be obstructed substantially.
(ii) Since the enlarged bubbles 10 are interposed between the upper light permeable plate 1 and the cooling liquid, effective cooling of the light permeable plates 1 is adversely affected and thereby proper function of the apparatus is degraded. In an extreme case, the apparatus is undesirably damaged. For this reason, practical use of the apparatus is limited only to a case where the apparatus is arranged with a vertical attitude, resulting in the applicable range of the apparatus being narrowed.
(iii) Since the apparatus has a low heat ray absorption rate (remaining within the range of about 10%), it is difficult to suppress thermal expansion of an object to be irradiated with a light, e.g., a printed circuit board. In addition, since the apparatus hardly absorbs harmful wavelength components other than the heat rays, there is a need of employing a discharge lamp which sufficiently matches with optical reactive characteristics of the photosensitive material.